U.S. patent application number 16/227394 was filed with the patent office on 2019-07-04 for method for controlling the elevation of a retaining device of a ground milling machine, and ground milling machine.
The applicant listed for this patent is BOMAG GMBH. Invention is credited to Michael GERHARDY, Steffen WACHSMANN, Jens-Martin ZEHBE.
Application Number | 20190203430 16/227394 |
Document ID | / |
Family ID | 66816710 |
Filed Date | 2019-07-04 |
![](/patent/app/20190203430/US20190203430A1-20190704-D00000.png)
![](/patent/app/20190203430/US20190203430A1-20190704-D00001.png)
![](/patent/app/20190203430/US20190203430A1-20190704-D00002.png)
![](/patent/app/20190203430/US20190203430A1-20190704-D00003.png)
![](/patent/app/20190203430/US20190203430A1-20190704-D00004.png)
![](/patent/app/20190203430/US20190203430A1-20190704-D00005.png)
United States Patent
Application |
20190203430 |
Kind Code |
A1 |
WACHSMANN; Steffen ; et
al. |
July 4, 2019 |
METHOD FOR CONTROLLING THE ELEVATION OF A RETAINING DEVICE OF A
GROUND MILLING MACHINE, AND GROUND MILLING MACHINE
Abstract
A method for controlling the elevation of a retaining device of
a ground milling machine as well as to a ground milling machine.
Essential for the invention is that the retaining device is held in
an initial position at a distance from the underlying ground and is
reset from a yield position.
Inventors: |
WACHSMANN; Steffen;
(Boppard, DE) ; ZEHBE; Jens-Martin; (Boppard,
DE) ; GERHARDY; Michael; (Boppard, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BOMAG GMBH |
Boppard |
|
DE |
|
|
Family ID: |
66816710 |
Appl. No.: |
16/227394 |
Filed: |
December 20, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E01C 23/127 20130101;
E01C 2301/00 20130101; E01C 23/088 20130101; E01C 2301/40
20130101 |
International
Class: |
E01C 23/088 20060101
E01C023/088; E01C 23/12 20060101 E01C023/12 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 29, 2017 |
DE |
10 2017 012 124.9 |
Claims
1. A method for controlling the elevation of a retaining device of
a ground milling machine, comprising the steps: a) holding the
retaining device in an initial position at a defined holding
distance above the underlying ground, so that the retaining device
is not in contact with the underlying ground; b) starting the
milling operation; c) if ground material presses against the
underside of the retaining device from below with a vertical upward
counterforce, maintaining the retaining device in the initial
position with a retaining force up to a defined maximum retaining
force; d) if the counterforce exceeds the maximum retaining force,
releasing the retaining device for vertical upward displacement and
a pushing of the retaining device upwards by the counterforce; and
e) returning the retaining device towards the initial position when
the counterforce falls below the maximum retaining force, wherein
the retaining device is returned no farther than to the initial
position of the retaining device.
2. The method according to claim 1, wherein at least one of the
following steps precedes step a): placing the retaining device on
the underlying ground and subsequently raising the retaining device
until the initial position at the defined holding distance of the
retaining device from the underlying ground is reached; measuring
an operating variable associated with the height adjustment of the
retaining device and setting the raised height of the retaining
device until a target value of the operating variable associated
with the height adjustment of the retaining device is reached that
corresponds to a reaching of the defined holding distance of the
initial position; measuring a distance variable that changes with
the height adjustment of the retaining device in relation to the
underlying ground and raising or lowering the retaining device
until a distance variable is reached that corresponds to the
defined holding distance of the initial position; and deriving an
actual raised state of the retaining device with the aid of
displacement sensors associated with lifting columns for traveling
devices and/or with the aid of a displacement sensor associated
with a lifting device of the retaining device and/or with the aid
of a position sensor of the ground milling machine, and raising or
lowering the retaining device until a target raised state of the
retaining device is reached that corresponds to the defined holding
distance of the initial position and/or until a target displacement
value of the displacement sensor associated with the lifting device
of the retaining device is reached that corresponds to the defined
holding distance of the initial position while considering
measurement data of the position sensor of the ground milling
machine.
3. The method according to claim 1, wherein a pressure force acting
in the vertical downward direction is actively applied in step c)
in addition to the weight of the retaining device in order to hold
the retaining device in the initial position at a defined holding
distance above the underlying ground.
4. The method according to claim 1, wherein step d) comprises
switching a pressure relief valve.
5. The method according to claim 1, wherein when there is a height
adjustment of lifting columns connecting traveling devices to the
machine frame, the elevation of at least one lifting column is
monitored, in that a correction factor is determined if the
elevation of the at least one lifting column is changed, and in
that the correction factor is used to adapt the position of the
retaining device in order to maintain the defined holding
distance.
6. The method according to claim 1, wherein the retaining device is
held in the initial position so that the defined holding distance
above the underlying ground lies in a range of from 5 to 50 mm.
7. A ground milling machine for carrying out the method according
to claim 1, comprising: a machine frame supported by traveling
devices; an operating platform, from which the ground milling
machine is operated; a milling device with a milling drum which is
arranged inside a milling drum housing and which is rotatable about
a rotation axis; a retaining device which is arranged in front of
the milling drum in the milling direction and which is
height-adjustable via an actuator; a drive engine, with which the
drive power required for the milling and traveling operation is
generated; wherein a positioning control unit is provided which
regulates the actuator of the retaining device in such a manner:
that it initially maintains the elevation of the retaining device
in an initial position at a defined holding distance above the
underlying ground during milling operation, so that the retaining
device is not in contact with the underlying ground; that it keeps
the retaining device in the initial position with a retaining force
up to a defined maximum retaining force when ground material
presses against the underside of the retaining device with a
vertical upward counterforce from below; that it releases the
retaining device for vertical upward displacement when the
counterforce exerted on the retaining device by the ground material
exceeds the maximum retaining force; and that it returns the
retaining device towards, but no farther than, the initial position
when the counterforce falls below the maximum retaining force.
8. The ground milling machine according to claim 7, wherein the
positioning control unit comprises a setting mode so as to comprise
at least one of the following features for raising the retaining
device to the initial position: it uses an elevation of the
retaining device when the retaining device is lowered to the
underlying ground; and/or it incorporates measuring an operating
variable associated with the height adjustment of the retaining
device and setting the raised height of the retaining device until
a target value of the operating variable associated with the height
adjustment of the retaining device is reached that corresponds to
the reaching of the defined holding distance; and/or it
incorporates measuring a distance variable that changes with the
height adjustment of the retaining device in relation to the
underlying ground and raising or lowering the retaining device
until a distance variable is reached that corresponds to the
defined holding distance; it incorporates deriving an actual raised
state of the retaining device with the aid of displacement sensors
associated with lifting columns for traveling devices and/or with
the aid of a displacement sensor associated with a lifting device
of the retaining device and/or with the help of a position sensor
of the ground milling machine.
9. The ground milling machine according to any one of claim 7,
wherein it has a display device on the operating platform of the
ground milling machine, which displays at least one of the
following operating states: the retaining device is in its initial
position; the retaining device is in contact with the ground; the
retaining device is pushed upward beyond its initial position.
10. The ground milling machine according to claim 7, wherein it has
a setting device on the operating platform of the ground milling
machine, with which at least one of the following settings can be
performed: setting the initial position of the retaining device;
setting the maximum retaining force; switching between a ground
contact mode and an initial position holding mode.
Description
FIELD
[0001] The invention relates to a method for controlling the
elevation of a retaining device of a ground milling machine as well
as to a ground milling machine.
BACKGROUND
[0002] Generic ground milling machines are known in the prior art,
for example from EP 3168367 A1 and DE 19726122 A1. Such ground
milling machines are used for milling road surfaces, in strip
mining operations, in stabilization and recycling applications in
street and roadway construction as well as in road surface
restoration. Depending on the field of application, such ground
milling machines are also referred to as cold milling machines,
surface miners, stabilizers or recyclers.
[0003] Ground milling machines of this type comprise a machine
frame supported by traveling devices with front and rear traveling
units. The traveling devices can be connected to the machine frame
at least in part by means of height-adjustable lifting columns, so
that the machine frame can be lowered and raised in relation to the
ground underneath. Also arranged on the machine frame is an
operating platform from which the ground milling machine is
operated. The ground milling machine further comprises a milling
device connected to the machine frame with a milling drum arranged
inside a milling drum housing, said milling drum being rotatable
about a rotation axis extending transversely to the working
direction. The rotation axis usually extends horizontally and
transversely to the main working direction. This is usually the
forward direction of the ground milling machine. Also provided is a
drive unit, usually a diesel combustion engine, which generates the
drive power required for the milling and traveling operations. The
ground milling machine is usually designed as a self-propelled
ground milling machine.
[0004] Possible variations exist, inter alia, with respect to the
arrangement of the milling device. In so-called rear-rotor milling
machines, the milling device can be arranged in the rear area, in
particular at the level of the two rear traveling devices. Such a
ground milling machine is described, for example, in DE 19726122
A1. Also known are so-called center-rotor milling machines, in
which the milling device is arranged between front and rear
traveling devices at a distance from the same in the main working
direction. Such a ground milling machine is disclosed in greater
detail, for example, in EP 3168367 A1.
[0005] Generic ground milling machines further frequently comprise
a transport device with which the milled material obtained during
the milling operation can be loaded, for example, onto a transport
vehicle. This can be done in the main working direction to the
front as well as to the rear or laterally.
[0006] An essential element of generic ground milling machines is
the milling device. This comprises a milling drum arranged inside
the milling drum housing. The milling drum housing usually
comprises delimiting walls to the sides in the form of so-called
side plates that are height-adjustable in relation the ground, a
front delimiting wall and a rear stripping plate, in order to
prevent milled material from flying around and to facilitate, as
far as possible, a complete removal of the milled material. In
generic ground milling machines, the provision of a retaining
device that is arranged in front of the milling drum in the milling
direction and that is height-adjustable via an actuator is also
known. Said retaining device can have, for example, overall a
structure like a sliding block, which closes off the front
delimiting wall comprising the milling drum housing to the front in
certain circumstances. The object of the retaining device is
primarily in particular to prevent ground material, in particular
clumps of the same, from being raised in front of the milling drum
in the milling direction in order to facilitate a reliable milling
operation as well as in particular a reliable breaking up of the
milled material inside the milling drum housing. The retaining
device is height-adjustable in the vertical direction. With regard
to the control of its elevation, the retaining device
conventionally skims over the underlying ground in a kind of
floating position during the milling operation and is raised
temporarily if necessary, as described, e.g., in DE 19814053 A1. It
is also known to press the retaining device against the ground with
increased force if necessary, as described in EP 3168367 A1. The
retaining device can also act as a mount for a conveyor belt.
[0007] The known systems for controlling a retaining device
described above are, however, disadvantageous inasmuch as the
retaining device, which usually scrapes over the underlying ground
in front of the milling drum throughout the milling operation,
wears out quickly, in particular the runners frequently provided on
the same, and additionally reduces the forward propulsion of the
ground milling machine.
SUMMARY
[0008] The object of the invention is thus to indicate a way to
reduce wear and tear on the retaining device and to further
optimize the milling process. At the same time, in particular the
formation of ground clumps during the milling operation should be
avoided or at least reduced.
[0009] The object is achieved with the method for controlling the
elevation of a retaining device of a ground milling machine and
with a ground milling machine according to the independent claims.
Preferred embodiments are indicated in the dependent claims.
[0010] The basic idea of the invention is, instead of keeping the
retaining device in a standard position in which it is in contact
with the ground or even pressed down against the ground during the
milling operation, rather to guide it over the underlying ground in
a slightly raised position throughout the milling process. This has
the advantage that any wear on the retaining device is reduced
considerably and at the same time the forward propulsion of the
ground milling machine is no longer reduced by a retaining device
permanently dragging on the underlying ground.
[0011] According to the inventive method, the retaining device is
thus held in an initial position at a defined holding distance
above the underlying ground in a step A) before the initiation of a
milling operation, so that the retaining device is not in contact
with the underlying ground. An essential aspect of this step is
thus that the underside of the retaining device facing the
underlying ground no longer rests on the ground surface but is
rather raised and held at the defined holding distance, which
designates a vertical distance from the ground contact side of the
retaining device to the underlying ground. The distance indicated
here relates to the unprocessed ground substrate. If the ground
milling machine is now moved in the working direction in a step B),
during which the milling process is initiated, the retaining
device, which is raised off the underlying ground in the initial
position, no longer scrapes over the underlying ground. The holding
distance here is selected so that the gap between the underlying
ground and the bottom edge of the retaining device, which is formed
when raising the retaining device, is relatively small, so that no
milled material, or at least no significant amount of milled
material, is conveyed to the front and out of the milling drum
housing. Such a slightly raised positioning of the retaining
device, which is the default setting, is advantageous in that it
leads to considerably less wear and, moreover, does not constitute
a resistance to the forward propulsion of the ground milling
machine in the main working direction.
[0012] The slightly raised positioning of the retaining device in
the initial position described above is generally maintained
throughout the milling process. However, if, in step C), a force is
exerted on the retaining device in a vertical upward direction,
which can occur, for example, when ground material, especially in
the form of clumps, is pushed from below against the retaining
device by the milling drum, which generally rotates inversely to
the main working direction, so that this material presses against
the underside of the retaining device from below with a vertical
upward counterforce, the retaining device is initially kept in the
initial position with a retaining force up to a defined maximum
retaining force in accordance with the invention. In other words, a
retaining force, which counteracts the upward counterforce exerted
by the ground material, is actively applied to the retaining
device. As long as the maximum retaining force is not exceeded, the
retaining device thus remains in its initial position. However, if
the vertical upward counterforce exceeds the maximum retaining
force, a release of the retaining device for vertical upward
displacement occurs in step D), and the retaining device is pushed
upwards by the counterforce. In other words, the retaining device
thus yields in the upward direction in this case and is further
raised from its initial position, i.e. is pushed by the material
into a position in which it is raised further. This scenario can
occur, for example, when the milling operation temporarily produces
exceptionally large clumps of material or the like. However, in
accordance with step E), the retaining device is returned towards
the initial position when the counterforce falls back below the
maximum retaining force, the retaining device being returned no
farther than the initial position, i.e. not to a lowered position
at the level of the unprocessed ground surface. Thus, if the
counterforce exerted on the retaining device by the ground material
decreases until it falls below the maximum retaining force, the
retaining device is pressed back downwards, however no farther than
to its initial position. This pressing in the downward direction as
well as the exertion of the retaining force can already be
effected, for example, by the mere weight of the retaining device.
Preferably, however, there is an active application of force on the
retaining device in the vertical downward direction, for example
with the help of the hydraulic height-adjustment system of the
retaining device.
[0013] Overall, the method according to the invention thus
facilitates a relatively low-wear operation of the retaining device
and at the same time an increased forward propulsion efficiency of
the ground milling machine.
[0014] Advantageous embodiments of the method according to the
invention relate inter alia to the positioning of the retaining
device in the initial position prior to the beginning of the
milling process. Various alternatives can additionally or
alternatively be used here. For example, step A) is preferably
preceded by a setting down of the retaining device on the
underlying ground and a subsequent raising of the retaining device
until the initial position at the defined holding distance of the
retaining device from the underlying ground is reached. The setting
down of the retaining device can be detected very reliably and with
simple means, for example by means of pressure sensors in the
hydraulic height-adjustment system of the retaining device. The
position in which the retaining device is resting on the underlying
ground thus corresponds to the zero position. From this position,
it can now be raised to the initial position in a defined manner.
This can occur, for example, as a function of an actuation distance
and/or time. Additionally, or alternatively, it is also possible to
measure an operating variable associated with the height adjustment
of the retaining device and to set the lifting height of the
retaining device until a target value of the operating variable
associated with the height adjustment of the retaining device is
reached, said target value corresponding to a reaching of the
defined holding distance of the initial position. Such an operating
variable can be, for example, an actuation distance of a lifting
cylinder of the retaining device or the like. To this end, it is
possible to use either the associated operating variable directly
or an actual raised position of the retaining device derived from
the associated operating variable. Additionally, or alternatively,
it is also possible to measure a distance variable that changes
with the height adjustment of the retaining device in relation to
the underlying ground, and to raise or lower the retaining device
until a distance variable corresponding to the defined holding
distance of the initial position is reached. This can occur, for
example, by means of a distance sensor, for example a laser- or
ultrasound-based distance sensor, which is mounted on the retaining
device or on a part that is adjustable together with the retaining
device, and which ascertains, directly or indirectly, an actual
distance of the retaining device from the underlying ground in the
vertical direction. Additionally or alternatively, it is further
possible that an actual raised state of the retaining device is
derived with the aid of displacement sensors associated with
lifting columns for traveling devices and/or with the aid of a
displacement sensor associated with a lifting device of the
retaining device and/or with the aid of a position sensor of the
ground milling machine, and the retaining device is raised or
lowered until a target raised state of the retaining device
corresponding to the defined holding distance of the initial
position is reached and/or until a target displacement value of the
displacement sensor associated with the lifting device of the
retaining device is reached, which corresponds to the defined
holding distance of the initial position, in particular while
taking into account measurement data of the position sensor of the
ground milling machine.
[0015] In order to keep the retaining device in the initial
position at a defined holding distance above the underlying ground,
a pressure force acting in the vertical downward direction is
preferably actively applied in step C) in addition to the weight of
the retaining device. This means that the maximum retaining force
exceeds the force exerted by the mere weight of the retaining
device in the vertical downward direction, in particular by a
factor greater than 1.3. In this manner, the load that can be
applied to the retaining device until the retaining device is
released for vertical upward displacement according to step D) is
increased, so that the case in which the retaining device is
released according to step D), which is intended for exceptional
situations only, occurs less often. This ensures an overall more
even milling process.
[0016] The maximum retaining force can be defined in various
manners. Particularly preferably, it occurs by defining a switching
threshold of a valve, in particular a pressure relief valve,
especially one that operates purely mechanically. Such a valve thus
switches when the counterforce acting on the retaining device in
the vertical upward direction produces a pressure level in the
hydraulic displacement system of the retaining device that exceeds
the switching threshold of the valve, in particular of the pressure
relief valve. It is also possible, however, to use an
electromechanically controlled pressure relief valve.
[0017] One reason for the variation of the position of the
retaining device in relation to the underlying ground is the
displacement of the retaining device in relation to the machine
frame of the ground milling machine, which usually occurs by means
of one or more hydraulic cylinders. Moreover, the front and/or rear
traveling units of generic ground milling machines are also often
connected to the machine frame via lifting columns, so that a
height adjustment of the lifting columns can be used, for example,
to set the milling depth of the ground milling machine and to
control the position of the machine frame in relation to the
underlying ground. However, an adjustment of these lifting columns
indirectly also causes a change in the position of the retaining
device in relation to the ground. The method according to the
invention thus works particularly well when the initial position of
the retaining device, i.e. its vertical distance from the
underlying ground, is maintained even when the lifting columns are
adjusted. It is thus preferable that, when a height adjustment of
lifting columns connecting traveling devices to the machine frame
occurs, the height position of at least one lifting column is
monitored; that a correction factor is ascertained if the elevation
of the at least one lifting column is changed; and that the
correction factor is used to adapt the position of the retaining
device in order to maintain the defined holding distance. This
correction factor is thus used to offset the change in the relative
position of the machine frame, and thus the relative position of
the retaining device, caused by the change in the adjustment
position of the lifting columns, so that the retaining device
remains in its initial position in relation to the underlying
ground, i.e. maintains the defined holding distance. The height
position of the at least one lifting column can be ascertained or
monitored, for example, via a suitable displacement sensor which
monitors and ascertains the position of two elements of the lifting
column that are moved in relation to one another. This can be, for
example, a cable sensor or also a capacitive displacement
sensor.
[0018] Specifically, the retaining device is preferably held in the
initial position in such a manner that the defined holding distance
above the underlying ground is in a range from 3 to 100 mm and in
particular from 5 to 50 mm. This distance refers to the vertical
distance of the bottom edge of the retaining device from the
surface of the underlying ground in the initial position, i.e. in a
state of the ground in front of the milling drum in which it has
not yet been influenced by the milling process. In this distance
range, the retaining device is not only raised to a sufficient
extent to avoid getting caught by smaller ground irregularities
commonly encountered, but is also not yet adjusted upwards to an
extent that would allow an uncontrolled ejection of significant
amounts of milled material in the milling direction to the front
and out of the milling drum housing.
[0019] Another aspect of the invention relates to a ground milling
machine, in particular a ground milling machine designed to carry
out the method according to the invention. Such a ground milling
machine comprises, in a manner known per se, a machine frame
supported by traveling devices, an operating platform from which
the ground milling machine is operated, a milling device with a
milling drum that is arranged inside a milling drum housing and
that is rotatable about a rotation axis, a retaining device that is
arranged in front of the milling drum in the milling direction and
that is height-adjustable by means of an actuator, and a drive
engine with which the drive power required for the milling and
traveling operation is generated. According to the invention, the
ground milling machine further comprises a positioning control
unit. The positioning control unit is designed so as to adjust the
actuator of the retaining device so that the actuator initially
maintains the elevation of the retaining device in an initial
position at a defined holding distance above the underlying ground
during the milling operation, so that the retaining device is not
in contact with the underlying ground. The positioning control unit
is further designed in such a manner that it keeps the retaining
device in the initial position with a retaining force up to a
defined maximum retaining force when ground material presses
against the underside of the retaining device from below with a
counterforce acting at least partially in the vertical upward
direction. Thus, instead of immediately yielding in the upward
direction upon being contacted from below by ground material, the
retaining device initially maintains its initial position.
According to the invention, the positioning control unit here is
designed so as to release the retaining device for a vertical,
upward adjustment if the counterforce exerted on the retaining
device by the ground material, e.g. clumps of material, exceeds the
maximum retaining force. To this end, the positioning control unit
can determine and monitor the counterforce currently acting on the
retaining device either directly, for example via a force sensor,
or indirectly, for example via pressure values from pressure
sensors in the hydraulic adjustment system of the retaining device,
and release the retaining device for upward displacement when the
maximum retaining force is exceeded. Alternatively, the positioning
control unit can also be designed to act purely mechanically in
this situation, for example by means of a mechanically actuated
pressure relief valve. It is also possible to use an
electromechanically actuated pressure relief valve. How far the
retaining device yields in the upward direction can also vary. The
retaining device is preferably pushed upwards while maintaining the
maximum retaining force, while the maximum displacement distance of
the retaining device is preferably limited by means of a mechanical
limiting stop. What is essential here is that, once the
counterforce falls back below the maximum retaining force, the
positioning control unit returns the retaining device to the
initial position and no further. The retaining device is then
lowered back to its initial position.
[0020] The positioning control unit is preferably designed so as to
comprise a setting mode. In the setting mode, the retaining device
is, usually prior to the commencement of the milling operation,
raised or moved into its initial position. To this end, the
positioning control unit can be designed to use an elevation of the
retaining device when it is placed on the underlying ground and
lifted from there to the initial position. Additionally or
alternatively, the positioning control unit can also use the
measurement of an operating variable associated with the height
adjustment of the retaining device, for example a sliding position
of an actuating cylinder of the retaining device, and, based on
this, adjust the raised position of the retaining device until a
target value of the operating variable associated with the height
adjustment of the retaining device is reached that corresponds to a
reaching of the defined holding distance. Additionally, or
alternatively, it is also possible to provide a measuring device,
which is used to ascertain the actual distance of the retaining
device from the underlying ground, while the positioning control
unit uses these values for the adjustment of the retaining device
to the initial position. For example, this can occur by means of a
distance sensor, e.g. a laser or ultrasound sensor, at the
retaining device or a part that is moveable together with the
retaining device. Additionally, or alternatively, the positioning
control unit can also be designed to use a derivation of an actual
raised state of the retaining device with the aid of displacement
sensors associated with lifting columns for traveling devices
and/or with the aid of a displacement sensor associated with a
lifting device of the retaining device and/or with the aid of a
position sensor of the ground milling machine. In this embodiment,
the positioning control unit can thus, for example, ascertain a
correction variable based on current raised positions of the
lifting columns which influence and change the position of the
retaining device in relation to the underlying ground.
[0021] The ground milling machine preferably comprises a display
device on the operating platform of the ground milling machine
which displays at least one of the following operating states. For
example, the display device can be used to signal that the
retaining device is in its initial position and/or is in contact
with the ground, i.e. is in the zero position and/or the retaining
device is pushed upwards beyond its initial position and/or has
traveled the maximum upward displacement distance, for example, by
hitting a mechanical limiting stop. The latter can be sensed, for
example, by means of a suitable contact sensor. In particular when
the retaining device is pushed upwards as far as it will go,
further signals can be displayed to the operator on the operating
platform, and/or an intervention in the control of the machine, for
example a work stoppage, can be triggered.
[0022] Individual requirements, and in particular also the optimal
initial position of the retaining device, can vary depending on the
underlying ground material. Therefore, a setting device is
preferably provided on the operating platform of the ground milling
machine which is configured to allow at least a setting of the
initial position of the retaining device and/or a setting of the
maximum retaining force and/or a switching between a ground contact
mode, in which the retaining device is guided so as to drag over
the underlying ground in a manner known per se in the prior art,
and a holding mode in accordance with the invention, in which the
retaining device is held in the initial position at a distance from
the underlying ground.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The invention is described in greater detail in the
following based on the examples shown in the figures, which show
schematically:
[0024] FIG. 1: a side view of a ground milling machine of the
center-rotor type;
[0025] FIG. 2: a side view of a ground milling machine of the
rear-rotor type;
[0026] FIG. 3: a frontal view of the milling device against the
milling direction with the retaining device in the initial
position;
[0027] FIG. 4: the frontal view from FIG. 3, in which ground
material contacts the retaining device in its initial position from
below;
[0028] FIG. 5: the frontal view of FIGS. 3 and 4, in which a clump
of ground material pushes the retaining device upwards beyond the
initial position;
[0029] FIG. 6: a schematic side view of the retaining device shown
in FIGS. 3 to 5;
[0030] FIG. 7: a flow chart of a method according to the
invention;
[0031] FIG. 8: a control loop for the illustration of the height
adjustment of the retaining device in response to the action of
external forces; and
[0032] FIG. 9: a flow chart for an adaptation of the initial
position when a lifting column is adjusted.
DETAILED DESCRIPTION
[0033] Identical or functionally similar components are designated
with identical reference numbers in the figures, while not every
recurring component is necessarily designated in every figure.
[0034] FIG. 1 shows a ground milling machine 1 of the center-rotor
type with a machine frame 4 supported by traveling devices 2 via
height-adjustable lifting columns 3. Arranged on the machine frame
4 is an operating platform 5, from which an operator located on the
operating platform can control the traveling and/or milling
operation of the ground milling machine 1. The ground milling
machine 1 further comprises a milling device 6 with a milling drum
housing 7 and a milling drum 8 (merely suggested in FIG. 1)
arranged inside the milling drum housing, as well as a conveyor
belt 9 with which milled material can be loaded onto a transport
vehicle. During milling operation, the ground milling machine
travels over the underlying ground in the main working direction A,
which in the present case is the forward direction of the ground
milling machine 1, and mills the material in the underlying ground
14 at a milling depth FT. The milling drum housing comprises a
retaining device 10 (merely suggested in FIG. 1) arranged in front
of the milling drum 8 in the main working direction A, lateral
shields 11, as well as a rear stripping shield 12, all of which are
height-adjustable in the vertical direction and at least partially
close off the milling drum housing to the front, the sides and the
rear, for example in order to prevent milled material from flying
around and to ensure a controlled transport of the material inside
the milling drum housing.
[0035] FIG. 2 shows a ground milling machine of the rear-rotor
type, reference being made here to the corresponding description of
the ground milling machine 1 according to FIG. 1 in this regard. In
contrast to FIG. 1, only the two rear traveling devices 2 are
connected to the machine frame 4 via height-adjustable lifting
columns 3 in the ground milling machine 1 according to FIG. 2. At
the front, the ground milling machine 1 according to FIG. 2 has
either a single wheel or a pair of wheels connected with each other
via a pendulum axle.
[0036] The ground milling machines 1 according to FIGS. 1 and 2
further comprise a positioning control unit 13, which controls and
regulates the height adjustment of the retaining device 12, as
explained in greater detail below.
[0037] FIGS. 3, 4 and 5 are front views of the milling drum 6
against the main working direction A. In FIG. 3, the retaining
device 10, which protrudes from the rest of the milling drum
housing 7 in the main working direction A and which is connected
here to a front delimiting wall 15 and is height-adjustable
together with the same in the vertical direction via two hydraulic
cylinders 16, is in its initial position. In this initial position,
the retaining device is, with respect to its bottom edge 17, which
in the present case is formed by runners, at a distance A in the
vertical downward direction from the surface of the underlying
ground 14. The retaining device 10 is thus in a slightly raised
position and is thus not in contact with the underlying ground 14.
In the present example, the specific distance A is 10 mm and can
usually lie in the value range indicated above. As is evident from
FIG. 3, the milling tools, which are arranged on the milling drum 8
behind the retaining device in the working direction A, engage the
underlying ground. The raised initial position of the retaining
device 10 is maintained by the two hydraulic cylinders 16, the
extended position of which is controlled by the positioning control
unit 13, as suggested by the dotted lines in FIGS. 3, 4 and 5.
[0038] During milling operations, it can occur that, due to the
milling drum rotating against the direction of rotation of the
traveling devices, ground material, in particular in the form of
ground clumps 18, is lifted in the vertical upward direction in
relation to the remaining ground surface and strikes the bottom
edge 17 of the retaining device 10 in its initial position from
below. This state is shown in FIG. 4. In this case, the positioning
control unit 13 can now be designed so as to apply a retaining
force which counteracts this vertically upward acting counterforce
exerted by the ground material, i.e. presses downwards in the
vertical direction, and thus initially keeps the retaining device
10 in the initial position.
[0039] However, if the counterforce produced by the ground material
rising in the vertical upward direction exceeds a defined maximum
retaining force, provision is made for the retaining device 10 to
yield in the vertical upward direction, as shown in FIG. 5. Here,
the retaining device is raised in relation to the remaining ground
surface of the underlying ground 14 by the additional amount A+
relative to the initial position. In the present example, the
extent to which the retaining device 10 can be pushed further
upwards beyond the initial position is limited by a mechanical
limiting stop. Provision is also made for the positioning control
unit 13 to continue to apply the maximum retaining force to the
retaining device 10 in the vertical downward direction by means of
the hydraulic cylinders 16.
[0040] If the counterforce applied in the vertical upward direction
by the ground material now falls below the maximum retaining force,
the retaining device 10, controlled by the positioning control unit
13, returns to its initial position and reassumes its initial
position shown in FIGS. 3 and 4. Thus, the retaining device 10 is
lowered in the vertical downward direction only as far as the
initial raised position in relation to the ground surface, and not
down to the ground surface.
[0041] FIG. 6 illustrates, as an example, further details of the
positioning control unit 13, as well as some essential elements of
the ground milling machine 1. In the present example, it comprises
several sensors 19, 20 and 21, the measuring signals of which are
transmitted to a processing unit 23 with suitable control software.
The sensor 19 is a displacement sensor integrated into the lifting
column 3. Such a displacement sensor can be integrated in each of
the provided lifting columns of the ground milling machine 1. With
the aid of these sensor data, the positioning control unit 13 can
thus ascertain the position of the machine frame and thus
indirectly the position of the retaining device (at least
partially). The sensor 20 is a distance sensor which is
height-adjustable together with the retaining device 10. The
distance sensor 20 thus ascertains the vertical distance of the
retaining device 10 from the underlying ground. The sensor 21 is a
displacement sensor inside the hydraulic cylinder 16 by means of
which the retaining device 10 is height-adjustable in the vertical
direction. In particular with the aid of this sensor, the
positioning control unit 13 can thus track how far the retaining
device 10 has been pushed upwards or downwards starting from a
known position. The processing unit 23 of the positioning control
unit 13 controls a hydraulic system supply unit 24 comprising, for
example, a pump, a pilot valve or the like. With the aid of the
hydraulic system supply unit 24, it is possible, for example, to
produce the additional retaining force beyond the force of gravity.
Alternatively, it is also possible to produce the retaining force
by switching a hydraulic valve to a blocking position when a
counterforce increases. Also provided is a pressure relief valve
25, which can be controlled, for example, by the processing unit 23
of the positioning control unit 13 or can also be designed to act
purely mechanically. Via the pressure relief valve 25, it is
possible, for example, to define the maximum retaining force
specifically by means of the switching threshold of the pressure
relief valve. FIG. 6 is to be understood merely as an example.
Additionally or alternatively, pressure sensors or similar sensing
means can, for example, also be provided inside the hydraulic
system supply unit of the hydraulic cylinders 16 and the lifting
columns 3.
[0042] FIG. 7 illustrates the essential method steps for
controlling the position of the retaining device in accordance with
the invention. A first essential aspect is that, in step 26, the
retaining device 10 is held in the initial position during the
milling operation, for example as described above. In the initial
position, the retaining device is raised in relation to the
underlying ground and is thus not in contact with the latter. Thus,
the retaining device 10 does not drag over the ground when the
ground milling machine 1 travels over the underlying ground in the
working direction A during the milling operation. Step 27 involves
starting the milling operation, which in the present case also
includes a continuation of a milling operation. Here, the retaining
device is still held in its raised initial position according to
step 26, in particular in relation to the machine frame. It can now
occur that the motion of the milling drum causes ground material to
rise from below and press upwards against the retaining device with
a counterforce. In the method shown in FIG. 7, step 28 then
involves initially maintaining the retaining device in its initial
position and applying thereon a retaining force, which is produced,
e.g., by the weight of the retaining device or also by additional
application of pressure by means of the hydraulic cylinder 16, and
which counteracts this counterforce. However, if the counterforce
exerted on the retaining device by the ground material in the
vertical upward direction continues to increase and a maximum
retaining force is exceeded, step 29 involves releasing the
retaining device so that it now yields by a displacement upwards.
This can include, for example, switching a pressure relief valve.
This yielding motion is usually limited in the vertical upward
direction, for example by means of a mechanical limiting stop. If
the counterforce exerted by the ground material pressing against
the retaining device in the vertical upward direction from below
now decreases enough to fall back below the maximum retaining
force, a returning of the retaining device towards the initial
position finally occurs in step 30. This returning movement is
limited in the vertical downward direction by the reaching of the
initial position of the retaining device. The retaining device is
thus not pressed down to the normal ground surface but only as far
as the initial position, in which the retaining device is
positioned at the defined holding distance A above the underlying
ground.
[0043] Prior to the method steps described above, step 31 can also
involve moving the retaining device to the initial position by
means of further measures of the method. For this purpose, it is,
for example, possible that, in order to ascertain the zero
position, i.e. the position in which the retaining device contacts
the ground surface, the retaining device is in step 31 initially
placed on the underlying ground, which can be ascertained, for
example, by a pressure fluctuation in the hydraulic system supply
unit of the hydraulic cylinder 16, and is then raised by a defined
distance, which can be measured, for example, with the aid of the
sensor 21, until it reaches the initial position. Additionally or
alternatively, it is also possible that the vertical distance of
the retaining device from the underlying ground is measured and
monitored by the distance sensor 20 and is ultimately used as a
target variable for the height adjustment of the retaining
device.
[0044] Each of the method steps described above can comprise the
use of a correction variable, in particular for defining and
monitoring the initial position of the retaining device, in the
control and regulation of the position of the retaining device
according to step 32. This can become relevant in particular when
the ground milling machine 1 has a machine frame that is
height-adjustable via lifting columns, since the adjustment of the
lifting columns also results in a change in the position of the
retaining device in relation to the underlying ground. In this
case, provision can be made for the positioning control unit 13 to
receive displacement data obtained via suitable displacement
sensors of the lifting columns and to consider these data for the
control and regulation of the position of the retaining device.
Additionally or alternatively, it is also possible here to use a
position sensor of the ground milling machine, with which in
particular the horizontal position of the machine frame is
monitored. Specifically, this can mean that, when the machine frame
is lowered by retracting the lifting columns, which also results in
a lowering of the retaining device indirectly connected to the
machine frame, the retaining device is raised by the amount of the
correction factor in order to remain in its initial position in
relation to the ground surface, i.e. in order to still have the
same vertical distance from the ground surface after the height
adjustment of the machine frame.
[0045] FIG. 8 now in particular illustrates further details of an
illustrative design of a control loop, in particular for the method
steps 28 to 30. The starting point according to 33 is the currently
set height of the retaining device in the vertical direction above
the surface of the underlying ground. Starting from the current
position, which is ascertained, for example, with the aid of one of
the sensors 20 or 21, the positioning control unit 13 conducts a
check 34 whether the current position of the retaining device
deviates from the initial position A in the vertical upward
direction (h>0). If there is such a deviation, the retaining
device remains in this floating position, if necessary with an
additional retaining force being applied. If, on the other hand,
there is no such deviation, according to 36, the retaining device
remains held or fixed in the initial position. At 37, a determined
position of the retaining device is updated. The current position
thus determined is fed back and the control loop described above is
run again. The process described in FIG. 8 can be performed by the
positioning control unit 13 continuously or also intermittently,
for example in a timed manner.
[0046] FIG. 9 illustrates further details for the adaptation of the
positioning of the retaining device or the determination of a
correction variable for the adjustment of the retaining device in
order to maintain the initial position, i.e. the vertical distance
of the underside of the retaining device from the underlying
ground, when the lifting columns 3, in particular in a ground
milling machine 1 as shown in FIG. 1, are adjusted. The starting
point here is a measurement 38 of the position of the lifting
columns 3, in particular at least the lifting columns 3 connecting
the traveling devices to the machine frame at the front right and
the front left, respectively. This measurement 38 can be performed
during the milling operation or also at the beginning of the
milling operation. If, in step 39, the positioning control unit 13
determines a change in the lifting height of the right and/or front
left lifting columns, the calculation of a correction factor or
correction variable occurs in step 40 for the adjustment of the
retaining device based on the new height information. For example,
if the front lifting columns have been retracted, the correction
factor is the correction variable by which the retaining device
needs to be raised in order to reassume its initial position, i.e.
the defined holding distance of the retaining device in relation to
the ground surface in the vertical downward direction. In step 41,
the retaining device is now raised or lowered based on the
determined correction variable. If, on the other hand, no change in
height is determined, the retaining device remains fixed in its
current raised position in step 42. Subsequently, the control loop
described in FIG. 9 is run again starting at step 38. It is
possible here to run the process described in FIG. 9 continuously.
However, the adaptive height adjustment of the retaining device due
to a height adjustment of lifting columns as shown in FIG. 9
preferably occurs only if the lifting columns are actuated. This
method also applies accordingly when the height of the rear lifting
columns and/or of the front and rear lifting columns of a ground
milling machine is adjusted.
* * * * *